In recent years, silent chains have been used for power transmission under high speed and high load conditions. In a typical silent chain, a number of link plates P, each bifurcated to provide a pair of teeth on one side, are arranged in interleaved layers connected to one another by connecting pins Q as shown in FIG. 3. On the bifurcated portion of each of the link plates P, two outside flank surfaces R1 function as meshing surfaces in an outer flank meshing silent chain, or two inside flank surfaces R2 serve as meshing surfaces in an inner flank meshing silent chain. In either case, the meshing surfaces mesh with sprockets, and transmit power from the chain to the sprockets or from the sprockets to the chain. Even if the pitch of the chain is extended, close contact between the link plate and the sprocket is maintained. Accordingly, these silent chains produce little noise, and are suitable for high speed operation and for applications in which quiet operation is required.
Since these silent chains are used at high speed and under high load, in order to improve wear-resistance, a sliding surface of a chain is provided with a coating of hard inorganic material such as titanium carbide (TiC), vanadium carbide (VC) or the like by a CVD process, a PVD process, spray coating, diffusion coating, or the like,.
To improve wear-resistance, it has been proposed to form, on a surface of a silent chain, a chromium iron alloy layer having diffused chromium carbide particles, so that the surface has enhanced hardness while maintaining toughness.
However, where a coating of the above-mentioned hard inorganic material was provided on the surface of a silent chain, several problems were encountered. The load on the coated surface, and the sliding speed, were extremely large, and when foreign substances such as worn powder and the like were increased as a result of the use of a lubricating oil on the coated surface over a long time, the coated surface served as a boundary, causing an increase in temperature. Oxidation of the coated surface resulted, and sufficient wear resistance could not be obtained.
As described in Japanese Laid-open Patent Publication No. Sho. 57-85967, when a chromium-iron alloy layer with diffused chromium carbide particles is formed on a surface of the silent chain by subjecting the surface to a chromizing process, the hardness of the surface is improved by the particles of chromium carbide. However, since the chromium-iron alloy layer forming a base coated layer is a metal, the layer does not have sufficient wear-resistance. Additionally, in recent years, improved wear-resistance has been required in silent chains used in engines because of demand for high speed operation and long service life.
Accordingly, the objects of the invention are to solve the above-mentioned prior art problems and to provide a wear-resistant coating having excellent lubricating oil-retention properties, and to provide a coated silent chain having excellent wear-resistance.